The silicon carbide (SiC) metal oxide semiconductor field effect transistor (MOSFET) is an attractive power switch component in many power electronics applications. The advanced and innovative properties of wide band-gap SiC materials provide switching transistors that exhibit better operational properties than silicon MOSFET devices or insulated gate bipolar transistor (IGBT) devices. For example, the SiC MOSFET device has far lower switching losses than a comparable Si-based transistor switch and can operate at switching frequencies two to five times greater than a comparable Si-based transistor switch. SiC MOSFETs further exhibit very low leakage currents, and this contributes to boosting system reliability and consistency, even when subject to elevated reverse voltages or temperature increases.
It is crucial to drive the SiC MOSFET in such a way as to facilitate the lowest possible conduction and switching losses. It is noted, however, that the absolute maximum rating (AMR) sets a maximum Vgs-on and minimum Vgs-off of the SiC MOSFET that are not symmetric. For example, the maximum Vgs-on may be +25V while the minimum Vgs-off is −10V. A conventional symmetric driving circuit producing, for example, a gate drive signal having a maximum voltage of +12V and a minimum voltage of −12V cannot properly and efficiently drive the SiC MOSFET. In this example, the maximum drive signal voltage of +12V for the driving circuit produces a Vgs-on that is not high enough for the SiC MOSFET to turn on with best performance and the minimum voltage of −12V for the driving circuit produces a Vgs-off that is outside of the AMR of the SiC MOSFET.
There is a need in the art for a level shifting circuit to convert an input signal having symmetrical voltage, such as pulse transformers, to an output signal having asymmetrical voltage suited for use in driving the gate of a SiC MOSFET with the AMR requirements of the transistor device.